Ultra high frequency transmitter



Feb. 21, 1939. j F H. KROGERl 2,148,165

ULTRA HIGH FREQUENCY TRANSMITTER Filed Aug. 31, 1935 4 sheets-sheet V1i .ATTORNEY Feb. 21, 1939.

FL H. KRoGl-:R

ULTRA HIGH FREQUENCY TRANSMITTER 'Filed Aug. 51, 1955 4 Sheets-Sheet 2- INVENTOR FRED. H. KROGER ATTORNEY BIAS Si Feb. 21., 1939.v F. H. KRoGl-:R

ULTRA HIGH FREQUENCY TRANSMITTER Filed Aug. 51, 1955 4 Sheets-Sheet 3 FRED. H. KROGER BY )fg ATTORNEY Feb. 21, 19159. y F. H. KROGER l2,148,165

' ULTRA ETGEl FREQUENCE TRANSMITTER l' Filed Au'g. 3l, 1935 4 Sheets-Sheet 4 Fig. 4d

mi@ mn/m e INVENTOR FRED. H. KRUGER ATTORNEY ented Feb. 21, 1939 UNITED STATES PATENT ori-Ice 2,148,165 ULTRA HIGH FREQUENCY TRANSMITTER Fred H. Kroger,

Delaware Y., assignor to a corporation of Application August 31, v1935, Serial No. 38,707

3S Claims.

rlhis invention relates to radio transmitting circuits, and more particularly to a novel mechanical arrangement of line frequency controlled oscillator circuit and power amplifier unit.

A primary object of the present invention is to provide a transmitter capable of operating with high efficiency on extremely high frequencies of the order of 60 megacycles and higher.

A more specific object is to provide a transmitter design which enables the paralleling of electron discharge devices to a greater degree than heretofore possible on such high frequencies, by means of which harmful effects such as may be due to parasitics etc. are avoided.

Another object is to enable extremely reliable frequency control of an ultra high frequency master oscillator circuit inra transmitter, without employing mechanical vibrating elements. For this purpose there is employed, among other things, 4a resonant circuit in the form of a low power factor frequency control line having substantially uniformly distributed inductance and capacity.

A further object is to provide ahighly stabilized transmitter which is substantially completely enclosed in a metallic container integral with the transmitter and which comprises a single ended oscillator and a power amplifier each employing a plurality of electron discharge devices, both oscillator and amplifier being characterized by a high degree of physical and electrical symmetry of circuit connections.

A still further object is to provide `a substantially vibrationless ultra high frequency transmitter which employs a low loss frequency control line equipped with means for maintaining the over-all length of the line constant despite temperature fluctuations, and also employing temperature compensation means for circuit elements used in conjunction with the line control.

Other objects are to provide a mechanical arrangement of oscillator and amplifier in a tra-nsmitter whereby the field outside the assemblage, due to the transmitter, is reduced to substantially zero, and to provide a design possessing maximum rigidity of the tuned circuits and assemblage.

From 4a broad aspect, the invention contemplates the use of a line controlled mast-er oscillator and power amplifier unit in the form of (Cl. Z50- 17) of the transmitter. A concentric line having uniformly distributed capacity and inductance and maintained constant in length by means of a rod of low temperature coefficient and bellows attachment is used for controlling the frequency of the oscillator. Such a concentric line arrangement per se is described more completely in my United States Patent No. 2,108,895, granted February 22, 1938. For the power amplifier it is preferred to employ a push-pull affair, each half of which consists of two electron discharge devices connected in parallel relation and so arranged that anyone or two devices can fail to take its load without interfering with the operation of the system.

A feature of the invention lies in the absolute symmetry, both physical .and electrical, of the connections and circuit elements used in the master oscillator and power amplifier circuits. This feature is accomplished, in brief, by arranging each electron dischargev device to have in effect its own independent circuit with respect to Vits associated input and output circuits, so that should any one device change its functioning, i. e., emission fail or change, there is minimum reaction on the other devices.

A further feature prevents the occurrence of parasitics by capacitively grounding the control grids of the oscillator devices by means of a metallic plate which is part of the control line circuit.

Another feature resides in the use of an alternative power amplifier output or tank circuit for the use of frequency modulation within certain band widths, rather than amplitude modulation.

A still further feature is the temperature compensation arrangement employed for compensating for factors other than the length of the low loss concentric line.

Other objects, features and advantages will appear in the subsequent detailed description which i's accompanied by drawings wherein;

Fig. 1 illustrates schematically, and partly in section, a transmitter circuit in accordance with the principles of the invention;

' Fig, 2 illustrates the equivalent electrical circuit for Fig. l, in conjunction with an input circuit;

Fig. 3 illustrates the temperature compensation feature for the condenser in circuit with the control line;

Fig. 4 illustrates a completed structural embodiment of the transmitter as used in practice;

Figs. fia, lb, 4c, 4d, 4e and 4f illustrate eX- plcded views of the parts of the transmitter shown in Fig, 4; and

Fig. 5 illustrates schematically the alternative power amplifier anode tank circuit for use with frequency modulation.

Referring to Fig. l, there are shown two electron discharge device oscillators O and O', each comprising a cathode, a control grid, and an an- For controlling the frequency of the oscillators there is provided a resonant circuit in the form of a low loss one-quarter wave length conner adequately described in my United States Patent No. 2,108,895, supra. Oscillators O and grids connected to the control line by means of very short grid leads GL and GL' which connect with plate 4 of the capacitor 4, 5.

Line I has an electrical to one-quarter of the length of the operating thus avoiding any possibility of parasitic oscillations. Since the frequency control line I 2 has no radiation resistance and very little electrical the frequency of the master oscillator devices O and O. O' are arranged in parallel relation in order to does not overload thepower supply.V

Each oscillator O and O is arranged to have tubes is equally divided. A source of supply +B1 maintains the anodes at a suitable positive potential. Inductor 3 is merely a choke to provide a direct current return path from the grids of the oscillator to the respective cathodes.

where along the inner conductor I, proper choke is supplied. Practically, the most eillcient and convenient point of connection between conductor l and inductor 3 is where the inner conductor has approximately zero radio frequency potential. Elements 28 and 29 serve as by-pass condensers.

From the foregoing, it will be seen that there is absolute symmetry, both physical and electrical, of the oscillator tubes O and O about the anode circuit of the oscillators but also to balance the devices and to control the amount oi' grid excitation of the oscillators.

The value of capacitor 4-5 determines what amount of power shall be dissipated in the line for a given amount of grid excitation on the oscillators. This capacitor requires temperature compensation and this feature is more fully described later in connection with Fig. 3.

In circuit with each coil i8 in the anode circuit of the oscillators O and C is a by-pass condenser 23. From each inductor i8 is a tap which supplies energy from the oscillators through a blocking condenser 22 to the grid circuit of the power anipliiier electron discharge devices PA, PA. The amount oi power in the amplifier grid tank circuit -i', 9*@ is determined by the position of the taps on. coils i8 in the anode circuits oi the master oscillators O, O.

ifi constitute the other side of Amplier tubes PA, PA', it will be observed, are shown in push-pull relation and are an even number in thorough neutralization of the coupling of the the electron discharge devices. Since devices PA, PA' are in push-pull and connected to capacitance Q ".CV, the polarity of plate 9 must be and is made equal and opposite to the polarity of plate il' with respect to ground, and this is eiected by making the capacitance oi- 9' tune out the inductances l@ and 'l which are equal to each other, and by having the inductor l" in parallel relation and tuned with capacitor 5-5- The adjustment of capacitances Eiand S-Q gives, for a proper ratio, the balanced condition desired for the grids of the power amplifiers. A choke coil 2@ is provided as a grid direct current return path.

Condensers 8, il are included in the anode grid circuits of the amplifier devices for obtaining neutralization in well known manner, each device having individual thereto a neutralization condenser. As will be observed from Fig. 1, the stators of these condensers 8, i3' are integral with the condenser plates 9-9' and extremely short leads carry the rotors to the tube connections. The anode circuits of the amplifier devices consist of connections 2l, 2l" and a tank circuit comprising condenser it and inductance i3, to the latter of which is coupled any desired load circuit, such as an antenna, through the transmission line coupling l'l. Any suitable source of anode supply such as +132 is used for supplying the proper potential to the anodes of the power amplifiers PA and PA through the radio frequency choke coil 25. Condensers i9, 28 and 29 are merely by-pass condensers.

It will be observed that there is the same degree of absolute symmetry, both physical and The dotted lines in Fig. l indicate the voltage distribution across the elements of the oscillator and power ampliiier circuits of the transmitter. The voltage distribution along element l shows the quarter wave length existing and inductor 3. The distribution of voltage along the elements 7', 7, 9 9', and Iii shows that the potentials on the two metallic plates of capacitor 9-9 are equal and opposite to each other.

iso

Fig. `2 shows the lequivalent `electrical circuit udiagraniofthe assemblage of Fig. l, and in addition, by way of example, any suitable input circuit comprising a source of audio frequency energy AF feeding a modulator device M whose output is coupled by way of an audio frequency modulation choke coil C tothe .center'or midpoint of the inductance `I3 for effecting amplitude `modulation of the output of the power amplifiers PA, PA. Although various ground connections have been shown in Fig. 2, it will be evident that these connections do not necessarily extend to earth, butto any point .of zero or fixed radio frequency potential, in accordance with standard practice.

It may be desirable to employ frequency modulation instead of amplitude modulation, in which case the transmitter does not have to contend with the limitation of the capacity of the power amplifier anode circuit to ground for audio frequencies. This particularly applies when the audio frequency is greater than 5 kc. With this limitation eliminated in frequency modulation, an alternative `power amplifier anode circuit is possible, and one such arrangement is shown in Fig". 5, which is identical with that of Fig. l except for that portion beyond the anode circuit of the power amplifiers. Referring to Fig. 5 in more detail, there are provided, in place of the elements Z'I, 2l', I3 and I4 of Fig. 1, which comprise, respectively, the inductances and the Vernier tuning capacitance for the power amplifierV anode circuit, elements Hill and IIBI for the indue-tance; elements `lllZ and IBS for the capacitance. The inductor H34 provides for feeding the anode circuit with D. C. supply. The dotted lines giving the potential distribution curves of illl, lili, m2, H13 show the result of this peculiar arrangement of elements. This arrangement, it is important to note, also follows the principle of symmetry outlined above in connection with Fig. -1.

An advantage of the arrangement of Fig. 5 is that it enables convenient tuning of the anode circuit and obtaininga balanced output with respect to the load.

Fig. 3shows an arrangement, of the type described in United States Patent No. 2,109,880 granted March 1, 1938, to Orville E. Dow, for compensating for temperature fluctuations of the capacitor 4, 5, which is in series with the frequency control line i. This arrangement, in conjunction with the invar rod and bellows arrangement, maintains `constant all factors which inuence the frequency of the oscillators.

In order to understand the operation of Fig. 3, it must be appreciated that the value of the capacitance 4,55 will vary with temperature inasmuch as the spacing of the dielectric between plates 4 and 5. will increase in proportion to the change in temperature.. and the area of the capacitor will increase as thesquare of the change in temperature. The resultant change, therefore, is an increase in capacitance proportional to the change in temperature. By providing a supporting rod` 2i which is appreciably longerl than other rod supports 26, .in themanner indicated in the drawings, there will be a resultant increase in the dielectric spacing with an increase of temperature. This resultant increase in spacing may be exaggerated by using for rod 2l a material of a greater temperature coefficient than the temperature coefficient of the material for 2li, or the converse may be provided. Thus the design enables the choice of dimensions and materials whereby the dielectric spacing Vof the capacitor will increase at a rate which will. just counterbalance the effect of the increase in area of: plates `land 5. If, in addition, there are found to be secondary effects, `these also can be eX- perimentally compensated for by the arrangement of Fig. 3. For a more detailed description of the operation of this feature, reference is made to the above mentioned Dow patent.

In practice, it is preferred to employ a plurality of compensation devices, as shown in Fig. 3, for controlling `the relative spacing between the metallic plates of the capacitor 4, 5. An arrangement illustrating the use of these compensating elements is shownin Fig. 4b, which shows.

only an exploded Ypart of a complete structural embodiment which has been used successfully in practice.

Fig. 4 illustrates7 in perspective, the mechanical design of a completed structural embodiment of an oscillator and power amplifier circuit of the type shown in Figs. 1 and 2. It will be noted that the entire radio equipment is completely shielded and mounted on helical springs S, S, in turn mounted on vertically supporting rods R, R so as to be mechanically vibrationless. In effect, the control line serves as a vibrationless support for the radio frequency circuit elements.

For a better understanding of the structural design of Fig. 4, reference is made to Figs. 4a to 4f, inclusive, which show various details of the transmitter, the same numerals being used as in Figs, l and 2 to indicate the same parts.

Fig. 4a shows only that portion of the completed transmitter which is below the plates o-f capacitor 4., 5. The inner conductor I of the concentric line is here shown raised slightly from' normal position to illustrate more completely the temperature compensation feature of Fig, 3, another vicw of which is shown in Fig. 4b. Fig. 4b shows a top view of the several temperature compensation units used in conjunction with capacitor 4, 5 and line I. Line I in this last figure is removed completely from thev surrounding outer conductor 2.

Fig. 4c shows the mechanical design of the portion of the transmitter between plate 5 of capacitor 4, 5 and metallic plate II. It should here be noted that inductances l', 'I and I!! are in the form of rods. Theouter metallic covering I2 for the parts of Fig, 4c is indicated in Fig. 4f which also shows metallic separating wings for shielding the tubes of the transmitter.,

Fig. 4d illustrates the design of the power amplier anode connections 21, 21 and the manner in which they connect with the output tank circuit comprising condenser I4 and inductance i3. Inductance I3 and bridge I5 here comprise straight elements.

Fig. 4e shows the covering cylinder I6 which surrounds the apparatus of Fig. 4d'. Line I1, shown in this figure, comprises straight elements which couple with inductance I3.

Referring again to Fig. 4, which shows the completed form of the transmitter, there is provided, in addition, a can-like arrangement 99 (shown partly broken away) which iits over the cylinders l5 and I2 and their associated elements to provide a completely shielded affair of outer symmetrical form. An aperture 98 to which a metallic pipe is normally attached enables the transmission line I'I to feed a load circuit.

From the foregoing, it will be appreciated that the invention is not limited to the precise arrangements of parts shown, since various modifications can be made without departing from the spirit and scope thereof. Also, the transmitter is not necessarily limited solely for use with radio since it is capable of use in any circuit wherein it is desired to employ an oscillator and amplifier circuit in accordance with the principles of the invention` What is claimed is:

1. In an ultra high frequency circuit, a resonant circuit in the form of a frequency control line having inner and outer concentric conductors, a plurality of electron discharge devices mounted on said line and connected in parallel relationship, each having an envelope containing within it a control electrode, said devices being located off the axis of said inner conductor, and connections symnietricaliy arranged from both a physical and electrical standpoint with respect to the axis of said inner conductor of said line coupled between said control electrodes and said inner conductor.

2. In en ultra high frequency circuit, a pair of electron discharge device oscillators connected in parallel relationship, eachdevice having an envelope containing within it a control electrode, a resonant circuit in the form of a concentric line having inner and outer concentric conductors for controlling the frequency of said oscillators, said devices being mounted on said line, and direct connections symmetrically arranged from both a physical and electrical standpoint with respect to the axis of said inner concentric conductor between the control electrodes of said oscillators and said inner conductor.

3. In an ultra high frequency circuit, a pair of electron discharge device oscillators each having a control electrode, a resonant circuit comprising a section of line having inner and outer concentric conductors for controlling the frequency of said oscillators, a condenser in series with the inner conductor of said line and a point of relatively xed radio frequency potential, and whose plates are symmetrically arranged from a physical and electrical standpoint with respect to the axis of said inner conductor, one plate of said condenser being connected to said inner conductor and another plate of said condenser being connected to a point of relatively fixed radio frequency potential, and direct connections symnietrically arranged with respect to the aids of sm'd inner conductor between the control electrodes of said oscillators and said inner con.

ductor.

4. In an ultra high frequency circuit, an oscillator, a resonant circuit in the form of a frequency control concentric line for controlling the frequency of said oscillator, an amplifier mounted on said line and having an input circuit, and connections symmetrical from a physical standpoint with respect to the axis of said control line between said input circuit and said oscillator.

5. In an ultra high frequency circuit, a pair of electron discharge device oscillators each having a control electrode, a resonant circuit in the form of a section of line having inner and outer concentric conductors for controlling the frequency of said oscillators, and direct connections symmetrically arranged, from both a physical and electrical standpoint, with respect to the axis of said inner concentric conductor between the control electrodes of said oscillators and said inner conductor, a plurality of electron discharge device amplifiers, and connections also symmetrically arranged with respect to the axis of said inner concentric conductor between said amplifiers and said oscillators.

6. A system in accordance with claim 1, characterized in this that said devices are oscillation generators.

7. A system in accordance with claim 5, characterized in this that said amplifiers are connected in push-pull relation.

8. A system in accordance with claim 5, characterized in this that said oscillators are connected together in parallel and two of said ampliers are connected together in push-pull relation.

9. An ultra high frequency circuit comprising an oscillator, a resonant circuit in the form of a section of line for controlling the frequency of said oscillator, an amplier coupled to said oscillator and mounted on said line, and an output circuit for said amplier comprising connections which are symmetrical, both physically and electrically, with respect to the axis of said line.

10. An ultra high frequency circuit comprising an oscillator, a resonant circuit in the form of a section of line for controlling the frequency of said oscillator, an amplifier mounted on said line and having input and output circuits, said input circuit being coupled to said oscillator, said input and output circuits comprising connections which are symmetrical both physically and electrically with respect to the axis of sai-d line.

11. An ultra high frequency circuit comprising an oscillator having an input circuit, a resonant circuit in the form of a section of line coupled to said input circuit for controlling the frequency of said oscillator, an amplifier mounted on said line and having an input circuit coupled to said oscillator and also having an output circuit, the input circuit of said oscillator and the input and output circuits of said amplifier comprising connections which are symmetrically arranged, both physically and electrically, with respect to th`e axis of said line.

12. An ultra high frequency circuit comprising an oscillator having an input and an output circuit, a resonant circuit in the form of a section of concentric line couple-d to said input circuit for controlling the frequency of said oscillator, an amplifier mounted on said line and having an input circuit coupled to the output circuit of the oscillator, said amplifier also having an output circuit, all of said input and output circuits being arranged symmetrically, both physically and electrically, with respect to the axis of said line.

13. An ultra high frequency circuit comprising an electron discharge device oscillator having a control electrode and a cathode, a section of line having concentric inner and outer conductors for controlling the frequency of said oscillator, said inner conductor having a length greater than one-quarter of the operating wave, a condenser in series with said inner conductor and a point of relatively fixed radio frequency potential, one plate of said condenser being directly connected to said inner conductor and to said control electrode, and another plate of said condenser being connected to a point of relatively xed radio frequency potential, and a connection from said inner conductor to said cathode, whereby parasitic oscillations are prevented.

14. A system in accordance with claim 13, characterized in this that said condenser is made variable.

15. An ultra high frequency circuit comprising a pair of electron discharge device oscillators whose inputs and outputs are connected in parallel relation, each of said devices having an anode, a control electrode, and a cathode, means connected in common to said control electrodes for stabilizing the output oscillations of said oscillators to a single frequency, a` connection from each anode to a common junction point, a variable tuning reactance in each connection for tuning the load between said oscillators, and a utilization circuit coupled to said junction point.

16. An ultra high frequency circuit comprising an electron discharge device oscillator having a control electrode and a cathode, a section of line having concentric inner and outer conductors for controlling the frequency of said oscillator, said inner conductor having a length greater than one-quarter of the operating'wave, a condenser in series with said inner conductor and a point of zero radio frequency potential, one plate of said condenser being directly connected to said inner conductor and to said control electrode, and another plate of said condenser being connected to a point of Zero radio frequency potential, and a connection from a point on said inner conductor to said cathode, whereby parasitic oscillations are prevented, and means connected to the plates of said condenser for varying the spacing therebetween to counterbalance the effect of an increase in area of said plates due to temperature fluctuations.

17. In an ultra high frequency circuit, a pair of electron discharge device oscillators each having an envelope containing a control electrode, a resonant circuit `in the form of a concentric line having inner and outer concentric conductors for controlling the frequency of said oscillators, said devices being mounted on and located off the axis of said line, and connections between the control electrodes of said oscillators and said concentric line, the elements of said oscillators and said connections being symmetrically arranged from both A a physical and electrical standpoint with respect to the axis of said inner concentric conductor.

18. An ultra high frequency circuit comprising two coaxial inductors in the form of straight rods having their adjacent ends separated from each other, a metallic plate connected to each of said adjacent ends to form a capacitor, a pair of push-pull connected electron discharge deviceseach having a control electrode, a connection from one of said control electrodes to one metallic plate and a connection from the other control electrode to the other metallic plate of said capacitor, said connections being symmetrical, both physically and electrically, with respect to the axis of said inductors, and means for supplying alternating current energy to one of said inductors.

19. A system in accordance with claim 18, including another electron discharge device in parallel relation to each of said push-pull connected devices, and similar symmetrical connections from said otherV devices to said inductors.

20. A substantially completely shielded ultra high frequency circuit comprising an oscillator circuit, a low power factor tuned circuit in the form of a section of line comprising inner and outer concentric conductors for controlling the frequency of said oscillator, said outer conductor comprising a metallic cylinder, and an amplifier circuit coupled to said oscillator and mounted Within said cylinder whereby said cylinder functions both as an integral part of, and as a shield for said high frequency circuit.

21. Asubstantiallycompletely shieldedultrahigh frequency circuit comprising an oscillator circuit, a low power factor tuned circuit in the form of a `section of line comprising inner and outer concentric conductors for controlling the frequency of said oscillator, said outer conductor comprising a metallic cylinder having a length greater than said inner conductor and extending beyond both ends of said inner conductor, and high frequency amplifier equip-ment mounted on said line and located Within an extension of said outer cylinder.

22. An ultra high frequency circuit comprising an oscillator, a section of line for controlling the frequency of said oscillator, an ampliner coupled to said oscillator, and an output circuit for said amplier comprising connections which are symmetrical, both physically and electrically, with respect to the axis of said line, said oscillator and amplifier being mounted on and supported by said line, and means for amplitude modulating the energy in said output circuit.

23. An ultra high frequency circuit comprising an oscillator, a section of line for controlling the frequency of said oscillator, an amplifier coupled to said oscillator, and an output circuit for said amplifier comprising connections which are symmetrical, both physically an-d electrically, with respect t0 the axis of said line, said oscillator and amplifier being mounted on and supported by said line, and means for frequency modulating the energy in said output circuit.

24. An ultra high frequency circuit comprising two coaxial inductors in the form of straight rods having their adjacent ends separated from each other, a metallic plate connected to each of said adjacent ends to form a capacitor, a pair of push-pull connected electron discharge devices each having a control electrode, a connection from one of said control electrodes to one metallic plate and a connection from the other control electrode to the other metallic plate of said capacitor, said connections being symmetrical, both physically and electrically, with respect to the axis of said inductors, and a connection including a capacitor coupling the remote ends of said inductors together, whereby said inductors and said two capacitors form a tuned circuit for said electron discharge devices.

25. An ultra high frequency circuit comprising two coaxial inductors in the form of straight rods having their adjacent ends separated from each other, a metallic plate connected to each of said adjacent ends to form a capacitor, a pair of push-pull connected electron discharge devices each having a control electrode, a connection from one of said control electrodes to one metallic plate and a connection from the other control electrode to the other metallic plate of said capacitor, said connections being symmetrical, both physically and electrically, with respect to the axis of said inductors, and a connection including an inductance coupling together the other end of one of said coaxial inductors with said other inductor, whereby both said inductors and said capacitor form a tuned circuit for said electron discharge devices.

26. In an ultra high frequency circuit, a tuned circuit comprising a section of line having inner and outer concentric conductors, .a plurality of electron discharge devices connected in parallel relationship, each having a control electrode, and connections symmetrically arranged from both a physical and electrical standpoint with respect to the axis of said inner conductor of said line coupled between said control electrodes and said inner conductor, and an output circuit for said devices Whose elements are also symmetrically arranged from both a physical and electrical standpoint with respect to the axis of said inner conductor.

27. In an ultra high frequency circuit, a tuned circuit comprising a section of line having inner and outer concentric conductors, a plurality of electron discharge devices connected in parallel relationship, each having a control electrode, and connections symmetrically arranged from both a physical and electrical standpoint with respect to the axis of said inner conductor of said line coupled between said control electrodes and said inner conductor, and a tuned output circuit for said devices comprising an inductor and a capacitor which are both also symmetrically arranged from a physical and electrical standpoint with respect to the axis of said inner conductor.

28. In an ultra high frequency circuit, a tuned circuit comprising a section of line having inner and outer concentric conductors, a plurality of electron discharge devices connected in parallel relationship, each having a control electrode, and connections symmetrically arranged from both a physical and electrical standpoint with respect to the axis of said inner conductor of, said line coupled between said control electrodes and said inner conductor, said connections being coupled to said inner conductor at points symmetrically displaced from the axis of said inner conductor.

29. In an ultra high frequency circuit, a tuned circuit in the form of a section of line having inner and outer concentric conductors, a plurality of electron discharge devices connected in parallel relationship, each having a control electrode, and connections symmetrically arranged from Vboth a physical and electrical standpoint with respect to the axis of said inner conductor of said line coupled between said control electrodes and said inner conductor, said connections being coupled to said inner conductor at points symmetrically displaced with respect to and on opposite sides of the axis of said inner conductor.

30. In an ultra high frequency circuit, a pair of electron discharge device oscillators connected in parallel relationship, each having a control electrode, a tuned circuit in the form of a section of line having inner and outer concentric conductors for controlling the frequency of said oscillators, and direct connections symmetrically arranged from both a physical and electrical standpoint with respect to the axis of said inner concentric conductor between the control electrodes of said oscillators and said inner conductor, said connections being coupled to said inner conductor at points symmetrically displaced with respect to and on opposite sides of the axis of said inner conductor.

31. An ultra high frequency circuit comprising a pair of electron discharge device oscillators whose inputs and outputs are respectively connected in parallel relation, each of said devices having an anode, a control electrode, and a cathode, means symmetrically connected in common to said control electrodes for controlling the frequency of said oscillators, individual connections from each anode to a common junction point which is` symmetrically positioned both from a physical and electrical standpoint from said anodes, individual variable tuning elements in each of said anode connections, and a utilization circuit coupled to said junction point.

32. High frequency apparatus comprising a tuned circuit having two inductors in the form of straight coaxial rods separated from each other by a capacitor in the form of two plates conductively coupled to the adjacent ends of said rods, said plates being symmetrically positioned physically with respect to said rods, and means located adjacent to but insulated from the other end of one of said rods for capacitively coupling together the remotely located ends of said rods.

33. High frequency apparatus comprising a shield in the form of a substantially completely enclosed metallic container, a tuned circuit in said container comprising two inductors in the form of straight coaxial rods substantially symmetrically arranged in the center of said container and separated from each other by a capacitor in the form of two plates conductively coupled to the adjacent ends of said rods, one of said rods having its other end conductively connected to one end wall of said metallic container, and the other rod having its other end capacitively coupled to the opposite end wall of said container.

34. High frequency apparatus comprising a tuned circuithaving two inductors in the form of straight, solid, coaxial rods separated from each other by a capacitor in the form of two plates conductively coupled to the adjacent ends of said rods, said plates being symmetrically positioned physically with respect to said rods, and means located adjacent to but insulated from the other end of one of said rods for capacitively coupling together the remotely located ends of said rods.

35. High frequency apparatus comprising a tuned circuit having two inductors in the form of straight, coaxially arranged conductors, said conductors being physically separated from each other at their adjacent ends to form a capacitive coupling between them, and a hollow continuous metallic conductor substantially surrounding both of said inductors over their entire lengths, 'said hollow conductor being directly connected to the other end of one of said inductors and capacitively coupled to the other end of said other inductor.

36. A substantially completely shielded Ultra high frequency circuit comprising an oscillator circuit, a low power factor frequency control tuned circuit comprising inner and outer concentric conductors for controlling the frequency of said oscillator, said outer conductor comprising a metallic cylinder, and an amplifier circuit coupled to said oscillator and mountedwithin an extension of. said cylinder, whereby said cylinder functions both as an integral part of, and as a shield for said high frequency circuit.

37. A short wave system comprising, in combination, a plurality of electron discharge devices each having an input and an output electrode within an envelope, a low loss tuned circuit in the form of a concentric line coupled to said input electrodes in parallel relationship, and a load circuit coupled to said output electrodes in parallel relationship, said electron discharge devices being mounted on said line.

38. A short wave system comprising, in combination, a plurality of electron discharge devices, eaoh having within an envelope grid and anode electrodes, a low loss tuned circuit in the form of a concentric line, and connections from the inner conductor of said line to like electrodes of said devices, said devices being arranged around and equidistant from the axis of said line, whereby the wiring to the electrodes of said devices is reduced to a minimum, said electron discharge devices being mounted on said line.

FRED H. KROGER.

(lil 

